An internal combustion engine, for example, a multivalve type internal combustion engine includes a dynamic valve mechanism which has two intake valves and two exhaust valves in one combustion chamber, the two intake valves being simultaneously opened and closed at a certain valve timing, and the two exhaust valves being simultaneously opened and closed at another valve timing.
As for the dynamic valve mechanism, there are many types of them such as a push rod type in which a push rod is used in order to increase reliability and degree of freedom for designing the configuration of a combustion chamber, a rocker arm type in which an overhead cam is used in order to increase degree of freedom for designing the configuration of the combustion chamber and to increase degree for designing the configuration of an intake hole, a swing arm system in which a swing arm is used in order to minimize the equivalent weight of a valve side of a dynamic valve system, and a direct drive system in which no rocker arm is used and a tappet is directly driven from immediately above the valve and is suitable for use in a high speed combustion engine having the highest characteristic number of vibration.
Also, as another dynamic valve mechanism, there is a mechanism having a circular conical contact surface with respect to a supporting member for supporting a rocker shaft and a rocker arm as disclosed in Japanese Utility Model Early Laid-open Publication Sho. No. 58-79004.
In the conventional dynamic valve mechanism of an internal combustion engine, as shown in FIGS. 5 and 6, a rocker arm 120 is disposed within a cam chamber 106 of a cylinder head 104 with one end thereof contacted with a valve stem end of a valve disc (not shown) and with the other end contacted with a cam portion 112a of a cam shaft 112. In order to swingably support the rocker arm 120, a rocker shaft 126 is thrust into a bearing portion 130 and a spring 142 of the rocker arm 120, and the rocker arm 120 is held by a holding portion 144 within the cam chamber 106. At this time, the side surface of the rocker arm 120 is urged against the side surface portion of the holding portion 144 by the energizing force of the spring 142 and the rocker arm 120 is positioned by the holding portion 144.
As a result, the conventional mechanism has a shortcoming in that because the holding portion 144 must be extended until it reaches the rocker arm 120, the thickness of the holding portion 144 in the axial direction with respect to the rocker arm 120 becomes large and, therefore, a large quantity of material is required when the holding portion 144 is manufactured and this is economically disadvantageous.
Also, it has a further shortcoming in that because of the large size of the holding portion 144, a large weight of the dynamic valve mechanism 110 of the internal combustion engine 102 is created. In addition, degree of freedom for carrying out layout of the dynamic valve mechanism 110 is limited and thus disadvantageous in actual use.
It is therefore an object of the present invention to realize a dynamic valve mechanism in an internal combustion engine in order to eliminate the above-mentioned shortcoming, which includes a rocker shaft for swingably supporting the rocker arm, a positioning portion mounted on the rocker arm and projecting in the axial direction of the rocker shaft, and a thrust bearing portion mounted on said cylinder head for supporting said rocker shaft through a holding portion thereof and projecting toward the rocker arm side in order to position the rocker arm by contact with the positioning portion. Owing to the foregoing construction, the quantity of material required at the time when the holding portion is manufactured can be minimized and this is thus economically advantageous. In addition, the dynamic valve mechanism can be made light in weight and degree of freedom for carrying out a layout of the dynamic valve mechanism can be enlarged.
In order to achieve this object, according tot he present invention, there is provided a dynamic valve mechanism in an internal combustion engine for opening and closing a valve body by swinging a rocker arm in accordance with rotation of a cam shaft, said dynamic valve mechanism in an internal combustion engine being characterized by including a rocker shaft for swingably supporting said rocker arm, a positioning portion mounted on said rocker arm and projecting in the axial direction of said rocker shaft, and a thrust bearing portion mounted on said cylinder head for supporting said rocker shaft through a holding portion thereof and projecting toward said rocker arm side in order to position said rocker arm by contact with said positioning portion.
Owing to the above-mentioned construction, at the time when the rocker arm is mounted, the rocker arm is swingably supported by the rocker shaft and this rocker shaft is carried on the cylinder head through the holding portion.
At this time, the positioning portion of the rocker arm is urged by the thrust bearing portion provided on the cylinder head, so that the rocker arm is positioned in a predetermined position.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will be described in detail with reference to the drawings wherein:
FIG. 1 is an enlarged sectional view of a portion of a dynamic valve mechanism of the present invention in an internal combustion engine.
FIG. 2 is a schematic enlarged view of the dynamic valve mechanism in an internal combustion engine.
FIG. 3 is a schematic plan view of the dynamic valve mechanism in an internal combustion engine.
FIG. 4 is a schematic sectional right side view of the dynamic valve mechanism in an internal combustion engine.
FIG. 5 is a schematic plan view of a prior art dynamic valve mechanism in an internal combustion engine, and FIG. 6 is a schematic sectional front view thereof.